The present invention relates generally to an ATM (asynchronous transfer mode) switch and a method for switching a path by the ATM switch. The present invention relates more particularly to an ATM switch and a method for switching a path by the ATM switch within an ATM switching equipment used for a broadband ISDN (Integrated Services Digital Network).
The broad ISDN is capable of offering a variety of media ranging from voices to moving pictures. Further, the ATM switching equipment transfers data on a cell-unit in an asynchronous transfer mode and is applicable to communications in a broad range from a low speed to a high speed.
Constructing a network for this broadband ISDN entails the use of the above ATM switching equipment. At an early stage of introducing the ATM switching equipment, there are small number of subscribers, and a small capacity of the switching equipment may suffice.
At a spread stage of the ATM switching equipment, however, the number of subscribers increases, and, hence the switching equipment is demanded of a large capacity. In this case, for the purpose of using the same switching equipment from the early stage to the spread stage, the switching equipment has to be expanded up to a large-scale switching equipment.
A method for expanding the ATM switch involves the use of an MSSR (Multi-Stage Self-Routing Unit). The MSSR is constructed by performing multi-stage connections of the SRMs (Self-Routing Modules) composed of small-scale switching modules for switching over paths on a cell-unit. Two methods for expanding the ATM switch exist.
According to a first method, all intermediate-stage SRMs of the switch are prepared from the beginning. For example, referring to FIG. 75, four pieces of intermediate-stage SRMs 1-12 to 1-42 are prepared from the beginning with respect to one first-stage SRM 1-11 and one rear-stage SRM 1-13. Further, in FIG. 76, the four intermediate-stage SRMs 1-12 to 1-42 from the beginning with respect to two first-stage SRMs 1-11, 1-21 and two rear-stage SRMs 1-13, 1-23.
Referring to FIG. 77, the four intermediate-stage SRMs are prepared with respect to the three first-stage SRMs and the three rear-stage SRMs. Turning to FIG. 78, the four intermediate-stage SRMs are prepared with respect to the four first-stage SRMs and the four rear-stage SRMs.
Next, according to the second method, a necessary minimum number of SRMs 1 of the first- and intermediate-stages as in the case of the rear-stage SRM 1 are prepared. For example, in FIG. 79, a single piece of SRM 1 is provided at each stage. Referring to FIG. 80, two pieces of SRMs are provided at each stage. Turning to FIG. 81, four pieces of SRMs 1 are provided at each stage.
Based on the first method, however, all the intermediate-stage SRMs are prepared from the beginning. Therefore, a hardware quantity increases even when a small-scale switch is constructed.
Further, according to the second method, an SRM-to-SRM path is switched when the SRM is expanded. This path switching operation is manually done and therefore very time-consuming.